Get Ready For Monarch Migration

If you spot monarch butterflies in your yard this month, there’s a good chance the eggs these insects are laying now will develop into the generation of adults that have made the monarch such an iconic species.

Beginning in late summer and continuing into early fall, monarchs that emerge from their chrysalides will be behaviorally and biologically different from generations that emerged earlier this year. Unlike their parents and grandparents, these late-season monarchs do not mate or lay eggs. Instead, the insects focus on feeding to fatten up for long migrations to their winter habitats: coastal California for monarchs west of the Rocky Mountains and central Mexico for those to the east. The great great grandchildren of butterflies that flew to breeding grounds last spring, these monarchs’ epic journeys—up to 3,000 miles—and large aggregations during winter represent one of the greatest natural history spectacles on the planet.

A monarch feeds on nectar from goldenrod in Rhode Island. Such late-blooming native plants are critical for fueling the insects’ fall migration. Photo donated by National Wildlife Photo Contest entrant Bernadette Banville.

Sadly, this spectacle is in danger of vanishing. Continuing a downward trend that began decades ago, the area of forest in Mexico occupied by monarchs last winter (2013-2014) shrank to just 1.65 acres, 56 percent of the previous year’s acreage (itself a record low) and the lowest figure tallied in two decades. During the mid-1990s monarchs filled almost 45 acres of Mexican forest. In California, the number of monarchs wintering along the coast has declined by nearly 90 percent since the mid-1990s.

One reason for such record-low numbers is that monarchs have been plagued by unfavorable weather events during the past two years, including heat waves, drought and, in 2013, an unusually cold spring and early summer that delayed the butterflies’ arrival in northern breeding grounds.

Habitat Loss on the Breeding Grounds

Monarch caterpillars munch on milkweed in Minnesota. Milkweeds are the only plants on which monarch butterflies lay eggs. Photo donated by National Wildlife Photo Contest entrant Margaret Hitchiner.

Beyond extreme weather—expected to worsen with climate change—several stresses have been hammering monarchs for many years. In Mexico, illegal logging and poorly regulated tourism in and around the butterflies’ overwintering sites have taken a toll, as has coastal development in California. To date most monarch conservation efforts have focused on safeguarding these winter refuges.

More recently, however, scientists have concluded that the most critical factor in the monarch decline has been habitat losson the butterflies’ breeding grounds, specifically destruction of milkweeds across huge swaths of the U.S. Midwest. The most recent evidence, published June 4 in the Journal of Animal Ecology, comes from a computer model developed by researchers at the University of Guelph revealing that habitat loss on U.S. breeding grounds, not on Mexican wintering grounds, is the most important cause of recent (and projected future) declines in monarch numbers. Monarch butterflies can lay their eggs only on plants in the milkweed family.

According to Chip Taylor, founder and director of Monarch Watch, midwestern milkweed losses have been fueled by massive conversion of grasslands, rangelands and former conservation reserves to monocultures of corn and soybean crops, a trend driven in part by pressure to develop biofuels. In addition, increased use of genetically engineered, herbicide-tolerant corn and soybeans throughout the region has allowed farmers to apply herbicides broadly, killing the milkweed that once thrived between crop rows and in fallow fields on millions of acres of agricultural land.

“Overall more than 20 percent of the monarch breeding habitat has been lost since the late 1990s, mostly in the Midwest,” Taylor says. “Monarch numbers will continue to decline unless the collective efforts of citizens, communities and governments are large enough to offset the annual loss of habitat.”

How You Can Help Monarchs

Newly emerged monarchs dry off on milkweed in Missouri. Beginning this month, monarchs will be laying eggs that develop into the species’ migratory generation. Photo donated by National Wildlife Photo Contest entrant Lisa Serda-Ansel.

Concern about monarchs, and about the plight of pollinators in general, has spawned several high-level efforts, including a proposal in May, endorsed by more than 50 researchers, farmers, educators and conservationists, to establish a multiagency monarch recovery initiative to restore the species’ habitat. In June, the White House released a presidential memorandum launching a federal strategy to protect monarchs and other pollinators.

Meanwhile, as a wildlife gardener, you can help monarch butterflies in your yard right now as the insects prepare for fall migration. Here’s how:

Plant milkweeds native to your region.

Depending on where you live, monarchs will be laying eggs for several more weeks, so it’s not too late to put in some milkweed. To find out which species are native or to purchase plants, check out Monarch Watch’s Milkweed Market, the Xerces Society’s Project Milkweed or NWF’s American Beauties native plant program.

Cultivate late-blooming, nectar-producing plants.

Avoid pesticides on monarch host and nectar plants.

In particular, steer clear of systemic insecticides such as neonicotinoids, which are taken up by the vascular systems of plants. This means butterflies and other pollinators can be exposed to poison long after a product has been applied by feeding on leaves, nectar and pollen.